Gain- and G/T-considerations on spaceborne active receive antennas

Multi-feed reflector antennas (MRAs) with suitable beamforming networks (BFNs) are the preferred solution for satellites in the geostationary orbit (GEO), since the GEO requires narrow beams with a limited scan range. For satellites in a low Earth orbit (LEO) direct radiating phased arrays can be attractive, since wider beams with larger scan angles are required in this case. The authors provide a general description for the most system-relevant parameters such as gain, noise temperature and G/T of an active receive antenna, which covers both MRAs and phased arrays and which is based on measurable antenna parameters. Apart from the use for system analysis and design, this description can be applied also to obtain useful specifications for such antennas and to provide some insight into their basic behavior in comparison to conventional passive types.